Offshore platforms are used in the drilling and production of oil, gas, and other hydrocarbons. To support the platform, pilings are driven into the soil underlying the body of water. The platform acts as a template to structurally interconnect the pilings and provides support for various equipment associated with the well. The platform typically consists of inclined main jacket legs, comparatively short satellite jacket legs, and cross braces which interconnect the legs. The main pilings generally extend upwardly from the soil and through the respective main platform legs. Satellite pilings typically extend from a point above the shorter jacket legs and down into the soil.
Static and dynamic axial, radial and rotational forces are transmitted from each piling to the surrounding leg, and from each leg to the interiorly positioned piling. The platform distributes loads from the main pilings to the satellite pilings and also distributes the other loads over each of the main pilings.
In order to provide the desired structural support between the pilings, it is essential that the platform legs be securely connected to the respective pilings. The desired structural connection is usually obtained by providing a pair of spaced inflatable members in the annulus between the piling and the platform leg. Concrete or other grouting material is then pumped into this annulus to connect the jacket leg to the piling. The cured grouting provides the necessary interconnection between the platform legs and the pilings to withstand the substantial axial, radial and rotational forces acting between the platform legs and the pilings.
In spite of the widespread acceptance of the above-described grouting technique, this procedure has significant drawbacks. The cylindrical-shaped pilings and external platform tubulars are rarely concentric, and it is difficult and expensive to ensure that grouting has adequately filled thinner annulus spacings between a platform leg and its eccentrically positioned piling. Most importantly, the grouting prevents the later separation of the subsea platform from its pilings during subsequent salvage operations after the economic life of the offshore wells served by the installation has been exhausted. While the pilings are metallic tubulars which can be cut below the sea bed mud line, the platform cannot thereafter be practically refloated to the surface because of the substantial weight which the pilings and the grouting add to the platform. As a consequence, platforms secured to pilings by the above-described grouting technique are customarily salvaged by cutting the platform into individual components which can be retrieved to the surface. This subsea disassembly of the platform is not only extremely expensive, but also substantially destroys the value of the platform for subsequent use.
Although grouting techniques are used in most petroleum recovery installations, platform legs have been mechanically connected to pilings by deformably expanding the piling radially outward until the piling contacts the platform legs. Equipment and techniques for radially expanding the pilings are marketed under the trade names "Lynes Corrigator" and "Hydrolock". This radial expansion technique is not widely accepted because of the expense and because the deformation of the piling inherently reduces the structural integrity of the piling. Moreover, this technique generally does not readily permit the retrieval of the platform, since the connection between the pilings and the platform legs cannot be practically disengaged.
Accordingly, a need exists for an apparatus and method for releasably connecting jacket legs of an offshore platform to pilings. The connection should be sufficiently secure to accommodate the large loading forces and should be readily detachable t permit recovery of the platform.